sir wm herschel infrared handbook - rg-cloud.com

Sir WM HerschelInfrared Handbook

P/N F2199 Rev C 06/11© 2011 Roberts-Gordon LLC

DRAFT

Table of Contents

1.0 Introduction to Radiant Heating......................................7 1.1 Story of Sir William Herschel...............................................7

1.2 What is Infrared?..............................................................81.3 The Electromagnetic Spectrum.............................................8 1.4 Utility of Infrared.............................................................91.5 Methodology of Radiant Heating Appliances.............................12

2.0 Types of Radiant Heating Equipment..............................152.1 ASHRAE Defi ned Types.......................................................152.2 Market Defi ned Types........................................................16

3.0 Concepts of Radiant Heating...........................................203.1 Thermal Effi ciency............................................................203.2 Emissivity.......................................................................253.3 Refl ectivity.....................................................................373.4 Convection Loss...............................................................383.5 Fixture Effi ciency.............................................................403.6 Pattern Effi ciency.............................................................403.7 Absorptivity....................................................................413.8 Radiant Effi ciency.............................................................453.9 Glossary of Terms.............................................................46

4.0 Radiant Heating Design Issues.........................................544.1 Utilization Factors............................................................544.2 Radiant Adjustment to Heat Loss..........................................584.3 Radiant Height Adjustment Factor.........................................58

5.0 Radiant Heating Application Issues..................................655.1 Parameters for Comfort......................................................655.2 Design Input Levels...........................................................675.3 Control Philosophy............................................................685.4 Installation Considerations..................................................715.5 Occupancy.....................................................................72

6.0 Fuel Utilization Analysis.................................................736.1 Formula Derivation...........................................................736.2 Illustrative Expense..........................................................79

7.0 Appliance Approach to the Market Place.........................837.1 Characteristics for Performance...........................................837.2 Appliance Comparisons......................................................85

APPENDIX: ANNUAL DEGREE DAYS............................................95

List of Figures and Tables

1. Electromagnetic Spectrum...........................................................10

2. Infrared Spectrum.....................................................................11

3. Energy Flow Chart - Radiant Heating..............................................13

4. Energy Flow Chart - Conventional Heating........................................14

5. ASHRAE Heater Types.................................................................17

6. Market Defi ned Heater Types........................................................19

7. Concepts of Radiant Heating........................................................22

8. Fundamentals of Combustion........................................................23

9. Stack Loss Calculation................................................................24

10. Nomograph for Determining Flue Loss with Natural Gas........................26

11. Nomograph for Determining Flue Loss with Propane HD-5.....................27

12. % of Total Radiant Output in Various Wavelength Bands for Black Body Radiation...............................................................................30

13. Emissive Power (W) at Varying Temperatures and Emissivities BTUH/FT2....21,32

14. EXCERPT.................................................................................33,34

15. Variations of the total normal emittance of Pyromark® coating with time of heating quiescent air........................................................35

16. Variations of the total normal emittance of Pyromark® coating as afunction of temperature.............................................................35

17. Comparison of the radiant fl ux density of Pryomark coating on as-rolled stainless steel 321 and on polished Inconel heated for 15 minutes at 2,000°F with Lambert’s cosine law for diffuse emission..........36

18. Confi guration comparison............................................................39

19. Absorption Ability for Water and Concrete........................................43

20. Absorbed Energy Comparison for water and concrete at Emitter Temperature of 9000°F (low intensity) and 1800°F (high intensity)..........44

21. Intensity Variation with Width......................................................56

22. Coverage Comparison.................................................................57

Figures

23. Burner Location for Intensity Charts...............................................60

24. Burner Layout for Intensity Charts..................................................62

25. Typical Range of Installed Capacity Requirements (BTU/FT2 - Hr) for Various Application Types........................................................68

26. Output Levels for Comfort in Spot or Area Heating..............................69

27. Correction Factor CD vs. Degree Days..............................................77

28. Fuel Utilization (U1) Factors.........................................................78

29. Job: “Sample Warehouse Cost Study”..............................................81

30. Comparative Equipment Analysis for 100,000 sq. ft. warehouse in Dallas, TX............................................................................82

31. Appliance Summary Table............................................................85

32. Appliance Comparison (A)............................................................86

33. Appliance Comparison (B)............................................................87

34. Appliance Comparison (C)............................................................86

35. Appliance Comparison (D)............................................................89

36. Appliance Comparison (E)............................................................90

37. Appliance Comparison (F)............................................................91

38. Distribution Layouts...................................................................92

1. Calculated Intensity Chart (single burner runs, high fi xture effi ciency equipment)................................................................59

2. Calculated Intensity Chart (multiple burner runs, high fi xture effi ciency equipment)................................................................61

3. Air Temperature required under various conditions to achieve comfort at (+o) of 70°F...............................................................67

4. *Action* for clothed Individuals (Air Velocity fpm)...............................70

List of Figures and Tables

Tables

1

Introduction to Radiant Heating

1.0 Introduction to Radiant Heating

1.1 Story of Sir William Herschel

An English astronomer discovered

infrared in 1800. Using a thermometer to

measure the heat of sunlight diffused through

a prism, he discovered that, whereas blue light

carried the least heat, the temperature on the

thermometer rises as the color changes to the

red spectrum.

It was actually beyond the red spectrum that

the highest temperature was reached - the

infrared spectrum.

Today’s scientists know that it is through this

range of infrared or “invisible” light waves,

that we receive about 50% of the sun’s energy.

In the late 1950’s, Roberts-Gordon pioneered the concept of gas-fi red infrared radiant tube heating which simu-

lates the direct rays of the sun. This principle results in substantial fuel economy. Infrared radiant heat energy is

directed downward to the occupants, the fl oor and building contents, warming them without warming the ceiling or

the air. Air heating then occurs by convection from the fl oor and the objects warmed by the infrared. This gas-fi red,

infrared, radiant tube principle of heating is one of the most economical and the most comfortable heating meth-

ods available today.

2


1.2 What is Infrared?

Infrared is the transmission of energy by means of electromagnetic waves (rays). When rays strike an object they

stimulate the molecules within the object, causing them to move rapidly and to generate heat. Infrared rays are

invisible and travel at the speed of light in straight lines from the heat source to all surfaces and objects without

heating the space (air), through which they pass. Energy in the rays is safely absorbed by cool surfaces (fl oors,

equipment, people), and conduction carries some of this heat deeper into surfaces creating a reservoir of heat.

The balance of the radiant energy is refl ected from heated surfaces to be absorbed by other cooler surfaces. The

temperature of air is raised by convection from heated surfaces.

Infrared heating equipment is most widely available today in two forms:

1. High-intensity equipment

2. Low-intensity equipment

High-intensity equipment, identifi ed by an open fl ame and high temperature (1800OF) ceramic surface, is what

many engineers associate with the term “infrared heat”. This type of equipment is more suitable to a localized

station heating or “spot” heating application and represents only a small portion of the infrared heating equipment

available to the heating system designer. Low-intensity equipment, identifi ed by a fl ame contained within a tube

or network of tubes at a reduced temperature (maximum 900O - 1000O F), is recognized as being an effi cient means

of heating an entire space. Heating a continuous span rather than a series of intermittent spots provides a level of

comfort surpassed only by the sun.

1.3 The Electromagnetic Spectrum

The electromagnetic spectrum differentiates all known types of electromagnetic wave energy via their wavelength

as measured in microns. The shortest wavelength energy (10-8 microns) known is the cosmic ray, while the longest

wavelength energy (5 x 108 microns) known is the broadcast radio wave.

Visible light falls between these two extremes having wavelengths between 0.4 and 0.7 microns. Infrared energy

waves are slightly longer than visible light, having wavelengths from 0.7 to 400 microns. However, the majority of

heat producing radiant energy falls within a much narrower wavelength range of 2 to 12 microns. It is important to

consider the heat energy wavelength for the following reasons.

a) The wavelength is directly related to the emitter source temperature, with higher temperature

sources generally producing a majority of the energy at shorter wavelengths.

b) The energy transfer to the solid body receiver can be affected by wavelength. Many materials more

completely utilize energy provided at longer wavelength (for example: concrete and water).

Page 4, Figure 1 illustrates the electromagnetic spectrum as it is known today.

3


Page 4, Figure 2 illustrates the infrared spectrum relative to common types of infrared heating equipment available

today.

1.4 Utility of Infrared

Radiant heating equipment has demonstrated its utilitarian nature in many diverse applications. Thousands of cost

effective installations exist in small automobile shops, as well as in large, high bay structures. To better understand

these results, it is necessary to review the manner in which a radiant heating appliance warms a space.

Infrared energy from a radiant appliance heats objects, people and surfaces, not the air. Certain elemental constit-

uents in the air (such as water vapor and carbon dioxide) do absorb radiant energy; however, the amount of these

substances is typically so small, that the heating effect on the air is negligible. The warm objects and fl oor convert

this energy to heat which:

• Is absorbed into the objects and fl oor creating a heat reservoir.

• Warms the air near the objects and fl oor via convection.

• Is reradiated to occupants and other surfaces of the space.

The radiant energy received by the occupants, directly from the heater or indirectly from the heater via reradia-

tion by the fl oor and objects, serves to increase the mean radiant temperature (MRT) of the occupant. In a man-

ner similar to direct sunlight, the increased MRT allows the occupant to perceive a comfort condition at a much

reduced air temperature (sometimes as much as 7O - 10O F lower). The resulting reduced air temperature within the

space provides the following advantages.

• Reduced stratifi cation of air within the space.

• Reduced actual transmission heat loss due to lower temperature inside than assumed design

condition as well as substantially lower ceiling and upper sidewall temperature due to reduced

stratifi cation (25° - 30° F lower is not usual).

• Reduced air change heat loss, to the extent that exfi ltration through cracks or openings, near the

roof, will be decreased due to decreased stack effect.

Each of the above advantages impacts favorably on fuel usage.

4


Electromagnetic Spectrum - Wavelength (microns)Figure 1

Figure 2

Infrared Spectrum - Wavelength (microns)

5


1.5 Method of Radiant Heating Appliances

All radiant heating appliances are not the same. Various material properties and performance criteria can be used

to evaluate a radiant heating appliance relative to its major function, namely:

• Provide usable radiant energy to the space in suffi cient quantity to provide comfort for the

occupants.

Page 7, Figure 3 is a visual representation of the factors that effect the performance of a radiant appliance. These

factors are reviewed briefl y below.

Natural gas(NG) or Propane(LP) fuel contains an inherent chemical heating value (approximately 1000 BTU/cubic

foot for natural gas(NG) and 2500 BTU/cubic foot for Propane(LP) gas). Of this total heating value available, only a

percentage is available to the radiant heating appliance, the remainder being stack loss.

This percentage is known as the thermal effi ciency and is described as follows:

Thermal Effi ciency = Total Input Energy - Stack Loss

Total Input Energy

The tube is heated by the available energy from the fuel gas. A tube material property, called emissivity, helps de-

termine the amount of energy that leaves the tube as radiant energy. The heat energy of the tube is dissipated by

one of the following mechanisms:

1. A portion of the energy is released as radiant energy directly to the space.

2. A portion of the energy is released as radiant energy and is refl ected by the fi xture to the space.

3. A portion of the energy from the tube is convected to the space.

4. A portion of the energy is released to the fi xture and “bounced back” into the tube.

The fi xture effi ciency is a measurement of the ability of the heating appliance to release radiant energy to the

space. Note that the relationships of items 1 through 4 above can greatly infl uence the fi xture effi ciency. Equally

infl uential to the fi xture effi ciency is the refl ector material and the refl ector shape. The property of the refl ector

material, known as refl ectivity, and the overall confi guration of the refl ector determine the amount of usable radi-

ant energy delivered to the space.

The pattern effi ciency of a radiant heating appliance is a measurement of the ability of a radiant heating fi xture to

deliver energy into a usable, specifi c distribution pattern in the space. It is this distribution pattern, together with

a material property of people or objects in the space known as absorptivity, that determines how much of the radi-

ant energy released by the heating appliance is utilized by the space to provide comfort to the occupants.

For comparison purposes, Page 8, Figure 4 provides a visual representation of the methodology for a conventional,

air heating appliance.

6


Energy Flow Chart - Radiant HeatingFigure 3

7


Energy Flow Chart - Conventional Air HeatingFigure 4

8

Types of Radiant Heating Equipment

2.0 Types of Radiant Heating Equipment

2.1 Ashrae Defi ned Types

All radiant heating appliances are not the same. A recognized method of classifying radiant heating systems is ac-

cording to the operating temperature of the emitting surface. For example:

1. High and Medium Intensity: above - 1500° F

2. Low Intensity: 500° F - 1500° F

3. Low Temperature: 120° F - 350° F

High and medium-intensity heaters usually take the form of open fl ame, non-vented appliances with incandescent

ceramic faces.

Low intensity units are designed to operate below incandescent temperatures and frequently use steel tube or pipe

as the emitter.

Low temperature radiant heating systems utilize large heated surfaces such as fl oors, walls, panels, or ceilings. The

surface temperature is elevated by hot water piping or electrical resistance wire embedded in the surface.

ASHRAE recognizes three specifi c types of infrared heaters that are gas fi red, See Page 10, Figure 5.

TYPE 1: Indirect Fired Units

Type 1 is characterized by burning a gas-air mixture inside a tube or enclosure, which radiates it’s

energy to the space. The products of combustion are generally vented to the outside. Typical

operating surface temperatures do not exceed 1200° F.

Type 1(a) units utilize an atmospheric burner venting products of combustion upward (for example:

patio heater).

Type 1(b) units utilize multiple vacuum assisted burners operating in a horizontal tube.

Type 1(c) units utilize a power assisted (forced draft) burner operating in a horizontal tube.

Type 2: Direct Fired Units

Type 2 is characterized by burning the gas-air mixture in a porous matrix of refractory material,

which radiates its energy into the space. The products of combustion are vented into the space.

Temperatures of operating Type 2 units range from 1600° F to 1800° F.

9


Type 3: Catalytic

Type 3 is characterized by mixing gas and air in the presence of a catalyst. The mixture oxidizes

without fl ame, and heat radiates into the space. The products of combustion are vented into the

space. Temperature of these catalytic units range from 650° F to 700° F.

2.2 Market Defi ned Types

The ASHRAE defi ned radiant heating appliance types do not adequately refl ect the recent evolution of new products

as available in the market place.

The result is that the industry has moved beyond these defi nitions by introducing new appliances that fall into more

then one of these categories. In addition, ASHRAE has not yet developed a way for the engineering community to

distinguish between appliance performances within a category or between categories.

The most visible demonstration of this defi nition inadequacy exists within the increasingly popular ASHRAE type

1(b) and type 1(c) appliance market. Recently introduced radiant heating appliances have many of the character-

istics of a type 1(b) system, but not all of them. Specifi cally, lower effi ciency systems do not provide for condensa-

tion of the combustion gases before exhaust.

Additionally, many manufacturers combine multiple, individual, non-condensing burner appliances on a common

exhauster and represent the resulting system as a type 1(b) condensing appliance. The lower effi ciency of these

systems more accurately refl ects the performance characteristics inherent in an ASHRAE type 1(c) appliance.

In order to differentiate these appliances, the market has defi ned a radiant heating appliance category in between

an ASHRAE type 1(b) and type 1(c). Burners in this category are referred to as Quasi type 1(b)/1(c) appliances or

multi-burner.

10


ASHRAE Heater TypesFigure 5

Type 3 - Catalytic

Type 2 - Direct Fired

Type 1(c)

Type 1(b)

Type 1(a)

11


Market history, as well, dictates differentiating approaches to the implementation of type 1(b), type1(c), and Quasi

type 1(b)/1(c) appliances.

Variation in market approach can be recognized as follows:

Description Appliance Type

• Engineered, custom designed, multiple burner, Type 1(b)

condensing appliances.

• Engineered, custom designed, multiple burner, Quasi type

non-condensing appliances. 1(b)/1(c)

• Factory assembled, single burner, non- Type 1(c)

condensing appliance.

• Site assembled, single burner, Quasi type

non-condensing appliances. 1(b)/1(c) or Type 1(c)

• Factory assembled, open fl ame. Type 2

• Factory assembled, catalytic combustion. Type 3

12


Market Defi ned Heater TypesFigure 6

Type 1(a)

Type 1(b)

Type 1(c)

Quasi Type/Multi-Burner

Type 3 - Catalytic

Type 2 - Direct Fired

13

Concepts of Radiant Heating

3.0 Concepts of Radiant HeatingAll radiant heating appliances have several component design and material factors affecting their performance and

utility. The factors include:

• Thermal Effi ciency

• Emissivity

• Refl ectivity

• Convection Losses

• Fixture Effi ciency

• Pattern Effi ciency

• Absorptivity

• Radiant Effi ciency

Understanding the importance of these factors, relative to the radiant heater performance, can insure the suitabil-

ity of a radiant heating appliance to a particular application.

While high thermal effi ciency (for example) is desirable, it is not the only factor contributing to a successful radiant

heating application. Following are additional areas that must be considered when determining the most suitable

radiant heating appliance for a particular application.

• The burner effi ciency and safety;

• The tube emissivity, temperature and total area;

• The refl ector angularity, inherent ability to trap hot air near the tube and material

refl ectivity;

• The absorptivity of objects or occupants within the space.

Each of these items infl uence the ability of a radiant heating appliance to provide comfort with a space. Defi cien-

cies in any of these areas can result in a poorly heated space or excessive fuel usage for a given comfort condition.

Following are in depth discussions of each of these important radiant heating concepts, See Page 15, Figure 7.

3.1 Thermal Effi ciency

Thermal effi ciency of a radiant heating appliance is defi ned as ratio of available energy output (at the point of use)

to total energy input, See Page 16, Figure 8. In practice, the thermal effi ciency can be determined by establishing

stack loss and utilizing the following formula:

Thermal Effi ciency = Total Input Energy - Stack Loss

Total Input Energy

14


Stack Loss can be determined by measuring the following:

a) Carbon Dioxide (C02) in fl ue gases (in % by volume)

b) Net fl ue gas temperature (defi ned as fl ue gas temperature - room temperature)

c) Latent heat recovered from water vapor in the fl ue gas when cooled to a temperature below

dew point.

For most fi eld test situations, it is impractical to determine c) above, and this contribution to stack loss is typically

ignored.

Once the CO2 % and net fl ue gas temperature are determined, a nomograph may be used to determine the stack

loss, hence the thermal effi ciency, See Page 17 Figure 9.

High thermal effi ciency is desirable, but because of the formation of condensate within a high effi ciency radiant

heating appliance, certain equipment design features are required to insure satisfactory longevity. ANSI Z83.6a

-1989 (test standard for gas-fi red infrared heaters) requires that suitable means be provided to prevent corrosion

and collect condensate formed in high effi ciency radiant heating appliances.

The argument to differentiate “wet” (condensing) or “dry” (non-condensing) radiant systems has centered around

the thermal effi ciency that will defi ne condensing or non-condensing operating conditions. Although ALL gas appli-

ances produce some level of condensate at start-up, an appliance is not considered condensing unless it continually

provides operational thermal effi ciencies above 83%. Although this thermal effi ciency does not provide a continu-

ously condensing environment, it does produce suffi cient condensate to cause corrosion in the appliance severe

enough to require that special design considerations to be employed to provide adequate operational life. The 83%

thermal effi ciency threshold is well documented in corrosion testing completed by a number of gas appliance indus-

try leading organizations including:

• Lennox

• Battelle Columbus Laboratories

• Gas Appliance Technology Center (GATC at Gas Research Institute (GRI)

• American Gas Association Laboratories (A.G.A.L.)

15



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Figure 8

Excess air in terms of the ideal air needed for complete combustion, can be calculated for most common fuel gases

as follows:

Excess air % = X 91

Where 91 is a constant for most fuel gases.

Ultimate CO2 for natural gas = 11.95%

propane gas = 13.78%

(Reference: Fundamentals of Combustion A.G.A. Laboratories, 1973)

Ultimate CO2 - Observed CO2

Observed CO2

Combustion of Methane and Air

17


Figure 9

Flue Loss CalculationsOn Page 24 and 25, Figures 10 and 11 are nomograph for use in calculating the fl ue loss (percent) of a hater operat-

ing on normally distributed gases whose characteristics falls within the following ranges:

Natural Gas Propane HD-5

Heater Value (gross), BTU per cu ft 970 - 1100 2466 - 2542

Specifi c gravity 0.57 - 0.70 1.522 - 1.574

Ultimate carbon dioxide (CO2), % 11.7 -12.2 13.73 - 13.82

In lieu of these nomograph or for a heater operating on normally distributed gases any of whose characteristics fall

outside of the range specifi ed above, the fl ue loss (percent) may be calculated from the following formula:

Where:

A = Air required for complete combustion, SCF per 1000 BTU of gas burned

C = Carbon Dioxide (CO2) in fl ue gases, percent of total dry constituents in the fl ue gases.

h = Relative humidity of air supplied for combustion, percent 100.

Lf = Flue loss, percent of heat input rate.

P = Dry constituents in fl ue gases from stoichiometric combustion SCF per 1000 BTU of gas burned.

T = Total constituents in fl ue gases from stoichiometric combustion SCF per 1000 BTU of gas burned.

Tf = Flue gas temperature, degree R.

Tr = Room temperature, degree R.

U = Ultimate carbon dioxide (CO2) of fuel gas percent.

REFERENCE: Z83.20 - 2001

18


An understanding of the corrosive nature of condensate and its relationship to thermal effi ciency is essential to

insure that radiant heating applications perform in the best interest of the consumer.

3.1.3 Marketplace Report - Thermal Effi ciency

Below is a summary of the range of thermal effi ciencies generally experienced within the industry. These are cat-

egorized by appliance type.

Appliance Type Thermal Effi ciency Rate

Type 1 (a) 70 - 75 %

Type 1 (b) 83 - 90 + %

Type 1 (c) 70 - 82 %

Quasi Type 1(b)/1(c) 70 - 82 %

Type 2 75 - 90 + %

Type 3 75 - 80 %

3.2 Emissivity

Emissivity is a material property commonly discussed with radiant heating appliances. It is a ratio of the amount of

infrared energy released by a material as compared to the amount that would be released by a black body surface

at identical temperature and conditions. A black body surface is a theoretical concept for an emitter having the

highest possible emissivity of 1.0.

The emissivity of a material is dependent on a number of factors.

• Temperature of the material: for many materials, variations in temperature produce signifi cant changes in the emissivity.

• Surface condition of the material: the emissivity characteristics of a material are determined mainly by the surface layers of material. For this reason, coatings can be applied to base materials to improve emissivity.

• Wavelength of emitted energy: for most materials, variations in emissivity can be expected to be dependent on the wavelengths at which the measurement was made.

It is important to note that high emissivity does not automatically provide high radiant energy output for a radiant

heating appliance. Emissivity is an indicator of the potential a radiant tube has to release energy. If, for example,

the refl ector on a radiant heating appliance can not direct energy released by the tube away from the appliance,

high emissivity serves no purpose. Additionally, this “bounced back” energy into the tube can increase tube tem-

perature, affecting emissivity, and creating the impression of increased heat release. Under these conditions this

energy release is typically overstated (when calculated).

A more meaningful measurement of the quantity of radiant energy released by a radiant appliance is known as

emittance.

Emittance is defi ned as the total energy released in radiant form over all wavelengths per unit area of surface,

19


Figure 10

Nomograph for Determining Flue Loss With Natural Gas(See text of exhibits A for usage limitations)

Reference ANSI Z83.20 - 2001

20


Reference ANSI Z83.20 - 2001

Figure 11

Nomograph for Determining Flue Loss With Propane HD-5(See text of exhibits A for usage limitations)

21


and is determined by four factors.

• Temperature of the emitting surface.

• Temperature of the surrounding surfaces.

• Emissivity of the emitting surface.

• Emissivity of the surrounding surfaces.

By determining the emittance of each unit area of a radiant heating appliance an estimate could theoretically be

made of the total radiant energy output from a radiant heating appliance using the Stefan - Boltzmann law. Note

that this would require accurate surface temperature, emissivity and area calculations for each unit area on a

radiant appliance, as well as similar information on each unit area of the surrounding surface. While this may be

possible in theory, the complex, dynamic nature of heat transfer phenomenon renders this approach impractical.

It is essential to recognize that radiant heating involves an EXCHANGE of energy between surfaces (for example, an

occupant and the fl oor). Understanding proper application of radiant heating equipment requires a realization of

the importance of this radiant exchange.

Page 29 and 30, Figure 13 provides a listing of theoretical emissive power (radiant output) of a surface at tempera-

ture shown for various emissivities. This Table is based on the Stefan - Boltzmann law as follows:

W = εσT4

Where: T = temperature

W = emissive power units

ε = emissivity of the material units

σ = Stefan - Boltzmann constant = 0.1714 x 10-8

Page 28, Figure 12 indicates the distribution of the emissive power as a function of wavelength for various tempera-

tures.

22


3.2.1 Market Report - Emissivity

Below is a summary of materials and emissivities generally available in the industry.

References

1. A.G.A. Research Bulletin #83

2. Radiative Transfer by Hottel and Sarofi n

3. Technical Letters, Inland Steel Corp.

4. Critical Table, National Bureau of Standards

5. Mark’s Std. Handbook for ME, 8th Edition

6. Literature from Manufacturer

A number of available radiant heating appliances utilize a silicone base high temperature paint (for example

Pyromark® manufactured by Tempil Division of Big Three Industries). These coatings are said to provide emissivi-

ties of 0.95. This value can only be achieved through proper air drying, oven curing and vitrifi cation of the coating

to inorganic silica, unlikely within the radiant heating industry. Even under these careful curing conditions, this

0.95 emissivity value cannot be achieved for surface temperatures much below 1800° F. This same, carefully cured

surface has an emissivity approximately equal to that of hot rolled steel at the same temperature (e = 0.8). Page 31

and 32, Figure 14 provides information on emissivity of high silicon resin paint from the manufacturer.

(wavelength)

MATERIAL EMISSIVITY @ TEMPERATURE REFERENCE

- Plain Steel 0.79 to 0.81 1000° F (3.6) 1,2,3

- Aluminized Steel (type 1) 0.20 to 0.50 1000° F (3.6) 3

- Aluminized Steel, heat treated (type 1) 0.80 1000° F (3.6) 3,4

- Fixed Ground coated steel 0.80 1000° F (3.6)

- Porcelainized Steel 0.92 to 0.96 100° F (9.3) 3,5

- Cast Iron 0.95 1000° F (3.6) 2

- Stainless Steel (type 304) 0.44 to 0.62 1000° F (3.6) 2

- Galvanized Steel 0.28 100° F (9.3) 2,4

- Calorized Steel 0.57 1000° F (3.6) 1,2

- Aluminum 0.02 to 0.05 100° F (9.3) 2,4

- Stainless Steel (type 430 polished) 0.10 to 0.20 100° F (9.2) 3,4

- Pyromark® Paint 0.80 1000° F (3.6) 6 (Silicon resin - properly cured and vitrifi ed)

23


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26


EXCERPT

(A portion of Pages 7, 8, 12, and 13 - plus all of Pages 19 and 20)

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION TECHNICAL NOTE D - 998

MEASUREMENTS OF TOTAL EMITTANCE OF SEVERAL REFRACTORY

OXIDES, CERMETS, AND CERAMICS FOR TEMPERATURES

FROM 600O F TO 2,000O F.

By William R. Wade and Wayne S. Slump

Reproduced by permission of NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Refractory Paints

Pyromark® paint - Included in the materials investigated was a refractory paint, Pyromark®, manufactured

by the Tempil Corporation (132 West 22nd St., New York, N.Y.). Although the exact composition of this paint is not

available from the manufacturer, it probably contains fi nely ground chromium oxide powders which produce a fl at

black. The paint may also contain a small amount of graphite, plus a silicate binder and an organic vehicle. An

X-ray diffraction analysis indicated only the presence of CrO. This paint is of interest because it will allow normal

metal forming and fabrication procedures that may not be possible with some other types of coatings.

For the Pyromark® coating, specimen preparation consisted of applying the paint in thickness of approximately

0.001 inch to solvent - cleaned metal strips of “as-rolled” stainless steel 321 and of polished Inconel. The coated

specimens were then air-dried at room temperature for at least 24 hours before testing. A preliminary investi-

gation to determine the adherence of this paint to a metallic substrate and the emittance stability at elevated

temperatures was conducted on both the stainless steel and Inconel specimens. This investigation indicated that

the Pyromark® coating has a high total normal emittance that remains essentially stable at temperatures up to

2,000O F as shown on Page 33, Figure 15. Visual examination of the test samples indicated no appreciable effort on

the coating after exposure to temperatures as high as 2,000O F for a period of 15 minutes.

Subsequent measurements of the total normal emittance for both the Inconel and stainless-steel specimens over

a temperature range from 600O F to 2,000O F are shown on Page 33, Figure 16. These curves indicate that slightly

different values of emittance may be obtained by applying the Pyromark® to different substrate materials, the

values increasing from 0.81 at 600O F to 0.94 at 2,000O F for the polished Inconel and from 0.78 at 600O F to 0.90 at

2,000O F for the as-rolled stainless-steel substrate.

Hamilton Boulevard • So. Plainfi eld, N.J. 07080

Figure 14

Division of Big Three Industries, Inc.

27


To determine whether the Pyromark®-coated specimens emit diffusely is accordance with Lambert’s cosine law, mea-

surements were made of radiant intensities from test specimens at angles of observation from 0O to 60O for a tem-

perature range from 600O F and 2,000O F are shown on Page 34, Figure 17, where the circle corresponds to Lambert’s

cosine law for perfectly diffuse emission. The close agreement between the measured values and Lambert’s cosine

law indicates that this coating emits diffusely for the temperatures and angles considered. Therefore, the measured

values of total normal emittance are close approximations of total head spherical emittance.

SUMMARY OF RESULTS

The investigation of chemically oxidized Inconel indicates that, although a high stable value of emittance may be at-

tained by this process, exposure to temperatures in excess of 1,600O F causes a change in the surface coating due to

the formation of another oxide. This change in the oxide results in a change of total emittance, limiting this coating

to fairly low temperature applications where stable emittance is desired. This measured values for this coating were

found to vary from 0.91 to 0.94 over a temperature range from 600O F to 1,600O F.

Results obtained for the paint coating tested, specifi cally chromium oxide paint (Pyromark®) and aluminum oxide

paint, indicate the coatings have high stable values of total emittance. The emittance values ranged from 0.78 at

600O F to 0.90 at 2,000O F for Pyromark® coating on “as-rolled” stainless steel 321 and from 0.81 at 600O F to 0.94 at

2,000O F for this same coating on polished Inconel.

Emittance measurements of a variety of silicon carhide and silicon nitride materials show fairly high values of total

emittance, which proved to be quite stable, after oxidation in air at 1,800O F. The measured values for these materi-

als show a decrease of emittance with increasing temperatures over the temperature range considered, a character-

istic of most ceramic materials. The total emittance for these stably oxidized materials varied from 0.94 at 600O F to

0.62 at 1,600O F.

The ceramics investigated were primarily chromium/aluminum oxide composites. Certain modifi cations of these

basic components result in three distinct materials which were designated by Haynes Stellite Co. as LT-1, LT-2, LT-LB.

These materials were all reported to have good thermal shock properties, resistance to oxidation and to mild abra-

sion, and high stable values of total emittance. The results of measurements conducted on these cerments show a

nearly linear increase of emittance over a temperature range from 600O F to 1,600O F, ranging from 0.76 to 0.94 for

the three materials tested.

Investigation of the total emittance conducted on fl ame-sprayed coatings of the cermets indicates that they can

have slightly higher values of emittance. The measured values for these coatings varied from 0.84 at 800O F to 0.94

at 1,800O F.

Langley Research Center, National Aeronautics and Space Administration, Langley Air Force Base, VA. Oct. 13, 1961

28


Variations of the total normal emittance of Pyromark® coating with time of heating in quiescent air.

Variations of the total normal emittance of Pyromark® coating as a function of temperature.

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Comparison of the radiant fl ux density of Pyromark® coating on as-rolled stainless steel 321 and on polished Inconel heated for 15 minutes at 2,000O F with Lambert’s cosine law for diffuse emission.

PYROMARK® is a product of TempilO Division So. Plainfi eld, N.J.

For literature and a 2oz. sample of black PYROMARK® write to:

REFRACTORY COATINGS DIVISION

Division of Big Three Industries, Inc.

HAMILTON BOULEVARD

SO. PLAINFIELD, N.J. 07080

Phone: 201.757.8300 Teies 138662

Manufacturers of TempestiasO TempilacO and TempilO Pellets

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600 OF 600 OF 2000 OF 2000 OF

30


3.3 Refl ectivity

Refl ectivity is a material property related to emissivity as follows

Emissivity + Refl ectivity = 1.0

It is a measure of the amount of energy redirected by a surface as compared to the amount that would be refl ected

by a prefect refl ector (a material having emissivity equal to zero).

Refl ectivity of a surface is dependent on a number of factors, the most important of which are as follows:

• Surface condition of the material: in a manner similar to emissivity, refl ectivity is mainly determined

by the surface layers of the material. A smooth, dense shiny surface generally produces highly

refl ective qualities.

• Wavelength of emitted energy: for most materials, some variations in refl ectivity can be expected as

wavelength changes. For infrared energy, this variation is small and is usually neglected. It is for this

reason that infrared radiant energy (particularly, long wave infrared energy) is considered essentially

“color-blind.”

The refl ector (or shade, as it is sometimes called) is a key component of a radiant heating appliance. In addition

to a highly refl ective material, the confi guration of the refl ector can effect the radiant output of the appliance as

follows.

• Overall depth of the refl ector can control the extent of convective loss from the appliance by

trapping hot air.

• Angularity of the refl ector determines the amount of energy directed away from the appliance,

evenly downward toward the occupied space.

31


3.3.1 Market Report - Refl ectivity

Below is a summary of materials and refl ectivities generally available within the radiant heating appliance

industry.

MATERIAL REFLECTIVITY**

- Tin 0.94

- Chrome 0.92

- Aluminum (mill fi nish) 0.91 to 0.95

- Aluminum (polished) 0.91 to 0.95

- Nickel 0.90

- Aluminized Steel (type 1) 0.50 to 0.80

- Galvanized Steel 0.72

- Stainless Steel (type 304) 0.48 to 0.66

- Stainless Steel (type 430 polished) 0.80 to 0.90

**References: A.G.A. Research Bulletin #83 and Critical Table, National Bureau of Standards

Page 38, Figure 17 indicates a number of refl ector confi gurations available throughout the industry. Consideration is

given to each confi guration regarding refl ectivity, angularity and ability to prevent convection losses.

3.4 Convection Losses

Convection is the transfer of heat from one point to another by moving and mixing masses of fl uid (either air or liq-

uid). Natural convection occurs when the motion is due to differences in density as caused by temperature differ-

entials. Forced convection occurs when the motion is imparted via mechanical means, independent of temperature.

Convection losses occur when a hot object is cooled by natural and/or forced convection. Convection loss of heat

from a radiant heating appliance causes a condition within the heated space referred to as stratifi cation. Building

heat stratifi cation, when experienced, often results in increased fuel usage as follows:

• Transmission heat loss is increased through the roof and upper wall areas by virtue of the increased

temperature difference from inside to outside.

• Air change heat loss in increased to the extent that there is ex-fi ltration through cracks or openings

in or near the roof as a result of the stack effect.

For convective heated spaces it is not unusual for ceiling and upper wall areas to be as much as 25O F to 30O F

warmer than areas near the fl oor. This can be controlled somewhat through the use of large circulating fans, how-

ever it should be noted that the electric power requirement for operation of these fans is substantial.

For buildings heated with radiant heating appliances, the subject of stratifi cation is essentially a non-issue, pro-

32


Figure 18CONFIGURATION COMPARISON

**Comparison Key: E = Above Average, A = Average, B = Below Average

33


vided the refl ector on the appliance traps hot air surrounding the radiant tube. Additionally, if the hot air is not

contained, a substantial reduction in radiant output may result due to cooling of the radiant tube. For example, a

reduction in tube temperature from 1100O F to 1000O F (a 9% decrease) can result in a radiant output reduction as

high as 23%.

3.4.1 Market Report - Convection Losses

Page 37, Figure 18 summarizes available refl ector confi gurations. It is important that the refl ector system

adequately prevent convection losses from the radiant heating appliance. While the practice of tilting

refl ectors is common in the radiant heating industry, the convection losses caused by this provide the same

negative effects on performance as described above. To properly redirect radiant energy to the sides of a

space, side extension shields are available from some manufacturers.

3.5 Fixture Effi ciency

Fixture effi ciency is a measurement index of the ability of a radiant heating appliance to release available radiant

energy to the heated space. All radiant heating appliance fi xtures absorb some infrared energy and convert it to

heat, which is convected away. An inability to control this convection loss, as well as the direction and distribution

of radiant energy results in a low fi xture effi ciency.

3.5.1 Market Report - Fixture Effi ciency

Fixture effi ciency is affected by many key components and properties of the components of a radiant

heating appliance. Clearly, high emitter temperature, high tube emissivity and high refl ector material

refl ectivity have a great infl uence on the fi xture effi ciency, however, a discussion of these areas without

consideration for tube length, refl ector shape, or the ability of the refl ector to control convective loss is

misleading. A determination of the effectiveness of a radiant heating appliance must include consideration

of all of these factors acting as a system in order to be accurate.

3.6 Pattern Effi ciency

Pattern effi ciency is a measurement index of the ability of a radiant heating appliance to distribute radiant energy

to the space in a manner consistent with the needs of the space. For example, consider a shipping dock. A rela-

tively high, localized, direct radiant appliance output level may prove effective in meeting the needs of the space.

In contrast, general comfort heating of a large space can be better served by a much lower evenly distributed

symmetric radiant appliance output. As illustrated, the pattern effi ciency of a radiant heating appliance is highly

subjective, and must be considered in concert with the application in question in order to be meaningful.

3.6.1 Market Report - Pattern Effi ciency

With the advent of numerous new products into the radiant heating market and the unavailability of

adequate industry standards to differentiate the market approaches, it is easy to understand the

34


confusion regarding suitability of one type of appliance versus another type in a particular

application. Resolution of the problem is possible if, as a fi rst step, the requirements of the space can be

identifi ed. Is it localized heating or general space heating? Do we want to warm people to comfort level or

just keep the fl oors dry? What are the ambient conditions? Is it drafty? Is the activity level high or low?

Answers to these (and many others) questions provide a strong design basis for a successful radiant heating

application.

Secondly, an understanding of the performance capabilities of the radiant heating appliance (its fi xture

effi ciency) is necessary to adequately match equipment to the requirement of the space. A single, larger

burner on a very long tube may provide adequate BTU, however, it may not provide suffi ciently even

coverage to be appropriate for the application. Only when the requirements of the space are matched to the

capabilities of the equipment can the heating equipment designer be assured of successful application of

radiant heating equipment.

Page 37, Figure 18 indicates relative pattern effi ciencies for various equipment confi gurations.

3.7 Absorptivity

Absorptivity is a material property commonly discussed with the application of radiant heating appliances to a

space. It is a measure (ratio) of the amount of radiant energy that can be absorbed by a material as compared to

the total radiant energy received by the material. For most materials, the absorptivity and the emissivity have

identical values.

Absorptivity is most important when considering the effect a radiant heating appliance will have on a space. Be-

cause some objects (for example: water, concrete and people) absorb varying wavelengths of radiant energy more

completely, it is important that the emitting radiant source produce the infrared energy in a wavelength that can

be best utilized by the space.

35

Concepts of Radiant Heating 3.7.1 Market Report - Absorptivity

Below is a summary report of major absorption wavelengths for miscellaneous materials.

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Page 41, Figure 19 illustrates average absorption ability for water fi lms and concrete in graphical form. By comparing

the wavelength of maximum absorption for these materials with the energy distribution for various wavelengths on

Page 29 and 30, Figure 13 of an estimate of the utilization of radiant energy from different source temperatures can

be made. Page 41, Figure 19 indicates that for an 1800O F emitter source (high intensity), approximately 78.7 % of the

emitted energy is absorbed by concrete and 28.3 % of the emitted energy is absorbed by water.

For a 900O F emitter source, (low intensity) approximately 83.8 % of the emitted energy is absorbed by concrete and

42.4 % of the emitted energy is absorbed by water.

3.8 Radiant Effi ciency

Radiant effi ciency is a measurement index of a radiant heating appliance comparing the actual radiant energy output

to the fuel energy input. Radiant output is a function of many system characteristics. Among these are:

• Emitter temperature

• Heat exchanger emissivity

• Total emitter surface area

• Fixture effi ciency

Large surface areas, together with high emissivity and uniformly high emitter temperatures provide the highest per-

centage of input as radiant output.

The ANSI standard for testing gas fi red infrared heaters (ASNI Z83.6a -1989) requires a minimum radiant effi ciency

of 35 %, however, for radiant heating appliances physically too large to have the radiant output measured according

to the method of test in the standard, this requirement is waved. Instead, a thermal effi ciency of not less than 70 %

must be attained (refer to sections 2.9.1 and 2.9.2 in ANSI Z83.6a-1989 for more information).

3.8.1 Market Report - Radiant Effi ciency

As discussed previously on Page 23, Section 3.2, the determination of radiant output from a radiant

heating appliance cannot be calculated in a practical (simple) manner. Manufacturer claims of radiant

effi ciencies of 55-60 % or more cannot be substantiated through measurement. Measurement is the

only way to insure accurate radiant effi ciency values. In order to make radiant effi ciency information

comparable for manufacturer to manufacturer, The Gas Research Institute and the Institute of Gas

Technology are developing a standard effi ciency measurement method for radiant appliances. Until

this work is complete, it is prudent to review so-called radiant effi ciency information thoroughly to

determine it validity.

39


3.9 Glossary of Terms

Absorptivity - An inherent property of a material evaluated by the ratio of the radiant energy absorbed to that fall-

ing upon it. It is equal to the emissivity for radiation of the same wavelength.

Air Change - (1) Introduction of new, cleansed, or recirculated air to a space. (2) A method of expressing the

amount of air movement into or out of a building or room in terms of the number of building volumes or room vol-

umes exchanged in unit time.

Air Shutter - An adjustable device for varying the size of the primary air inlet(s).

Aluminized Steel - Steel having resistance to oxidation due to formation of an aluminum/aluminum allow coat-

ing by hot dipping, hot spraying or diffusion processes. Emissivity typically 0.2-0.5 (unheat treated), 0.7-0.8 (heat

treated).

Ambient Air - The surrounding air (usually outdoor air or the air in an enclosure under study).

Annual Fuel Utilization Effi ciency (AFUE) - The ratio of annual output energy to annual input energy which in-

cludes any non-heating season pilot input loss.

Atmospheric Burner - A device for the fi nal conveyance of the gas, or a mixture of gas and air at atmospheric pres-

sure, to the combustion zone.

Black Body - (1) A body that absorbs all the radiant energy falling upon it. (2) A body that has the maximum theo-

retical radiant energy emittance at a given absolute temperature.

British Thermal Unit (BTU) (AN I-P UNIT) - The heat energy in a BTU was defi ned by the Fifth International Confer-

ence on the Properties of Steam (1956) as exactly 1055.055 852 62 J. It was related through specifi c heat to the IT

calorie so that 1 cal/kg K = 1 Btu/lb F for 1 lb = 453.592 37 g. The mechanical equivalent energy of a Btu is approxi-

mately 778.169 262 ft lb. The heat energy of a Btu is approximately that required to raise the temperature of a

pound of water from 59O F to 60O F.

Burner Control Assembly - An assembly of various valves, burner head, ignition system, fi lter, etc. necessary to

operate and control the burner.

Burner, End - The burner control assembly installed at the end of a series of burners farthest from the vacuum

pump.

Calorie - Heat required to raise the temperature of 1 gram of water 1 degree Celsius, specifi cally from 4O C to 5O C.

Mean calorie = 1/100 part of the heat required to raise 1 gram of water from 0O to 100O C. Great calorie or kilocalo-

rie - 1000 calories.

40


Calorized Steel - Steel having resistance to oxidation due to heating in an aluminum powder at 1472O F to 1832O F.

Emissivity typically 0.6.

Chimney - One or more passageways, vertical or nearly so, for conveying fl ue gases to the outside atmosphere.

Chimney Effect - The rising of air or gas in a duct or other vertical passage, as in buildings, inducted when the

density of air in the chimney is lower than that of surrounding air or gas.

CLO - A non-SI unit of clothing insulation defi ned as the thermal insulation necessary to keep a sitting person

comfortable in normally ventilated room at 70O F (21O C) and 50 % relative humidity. In physical terms, the thermal

resistance of one CLO - 0.88 F-ft2h/Btu (0.155 K m2/W).

Combustion Air - The air required for complete combustion of fuel, and usually consisting or primary air and, ex-

cess air.

Combustion Chamber - A 20 inch long section of 4” tubing with a top fi tting to accept a burner. A window is pro-

vided to observe the fl ame.

Combustion Chamber, End - A combustion chamber that received the fi rst burner in a series of burners. (Farthest

from the vacuum pump).

Comfort Chart - A chart showing dry-bulb temperatures , relative humidities and air motion so the effects of the

various conditions on human comfort may be compared.

Comfort Zone - A condition in an environment or enclosure whereby a suitable operative temperature is main-

tained. The required range of operative temperature for human comfort is defi ned by the comfort chart (refer to

ANSI 55-1981).

Condensate - Liquid formed by condensation of a vapor. In combustion of hydrocarbon fuels, water condensed from

fl ue products (this is typically slightly acidic). NOTE: Combustion of natural gas produces 11.2 gallons of condensate

for each 1 x 106 BTU burned. Combustion of propane gas produces 8.9 gallons of condensate for each 1 x 106 BTU

burned. Condensation begins at/below the dew point.

Condensation - The change of state of vapor into a liquid by extracting heat from the vapor.

Conduction (Heat Conduction) - Process of heat transfer through a solid.

Control, Single Stage - A control that cycles a burner from the maximum heat input rate and off.

Convection - (1) Transfer of heat by a fl uid moving by natural variations in density. (2) Transfer of heat by the

movement of a fl uid.

Forced Thermal Convection - Heat transmission by mechanically induced movement of fl uid.

41


Free Thermal Convection (Natural Convection) - Heat transmission by movement of a fl uid caused by density dif-

ference.

Coupling - A device used to connect sections of tubing. A standard unlines coupling is used to connect radiant

tubes.

Coupling, Damper - A coupling with a damper. This is installed where needed to adjust the vacuum in system.

Coupling, Lined - A coupling lined with Inconel. It is used to connect tail pipe tubes.

Decorative Grille - A 1/2” square honeycomb grille installed below the radiant tube. This is for decorative purposes

only. A 1-foot wide model installs directly on the refl ector. A 2-foot wide model installs in a suspended ceiling.

Degree Day - A unit of accumulated temperature departure, based on temperature difference and time. Used in

estimating fuel consumption and specifi cally nominal heating load of a building in winter. For any one day, the num-

ber of degree days of temperature difference between a given base temperature usually 65O F (18.3O C and 18O C in

Canada) and the mean outside temperature over 24 hours.

Direct Exhaust System - A mechanical venting system supplied or recommended by the manufacturer through

which the products of combustion pass directly from the furnace, heater or boiler to the outside which does not

employ a means of draft relief.

Direct Vent System - A system consisting of (1) a central furnace, heater or boiler for indoor installation, (2) com-

bustion air connections between the furnace, heater or boiler and the outdoor atmosphere. (3) fl ue gas connections

between the furnace, heater or boiler and the vent cap, and (4) vent cap for installation outdoors, supplied by the

manufacturer and constructed so all air for combustion is obtained from the outdoor atmosphere and all fl ue gases

are discharged to the outdoor atmosphere.

Draft Hood - A device installed on gas-fi red appliances designed to protect the appliance from chimney draft distur-

bances.

Dry-Bulb Temperature - The temperature of air indicated by an ordinary thermometer.

Dual Fuel Burner - A burner designed with two separate orifi ces and gas trains for both pilot gas fl ow and main gas

fl ow. This permits a fuel conversion to be made by selective energizing of the gas trains (i.e. and without physical

change of orifi ces).

Effi ciency - The ratio of the energy output to the energy input of a process of a machine.

Effi ciency, Thermal - The ratio of the useful/available energy at the point of use the thermal energy input over a

designated time.

42


Effi ciency, Radiant - The measure of the percentage of gross BTU input that is realized/available as direct radiant

BTU output.

Emissivity (e) - The ratio of the total amount of radiant energy emitted by a body to that omitted by a perfect

black body at the same temperature. (Perfect black body emissivity (e) = 1, perfect refl ector (e) = 0.).

End Vent Plate - A plate (approx. 4” dia.) that is attached to the end combustion chamber. This plate is pre-drilled

and the correct size must be installed to match the burner. This is used with or without outside air system.

Excess Air - In combustion, the percent or air greater than that required to completely oxidize the fuel.

Flow Unit - The amount of fuel-air mixture required for fi ring the rate of 10,000 BTU per hour. The would equal

1.83 SCFM. Flow units are used as a measure of fl ow rate for both combustion air and the air entering through the

end vent.

Flue - The general term for the passages and conduits through which fl ue gases pass from the combustion air and

the air entering through the end vent.

Flue Gases - Productions of combustion and excess air.

Flue Losses - The sensible heat and latent heat above room temperature of fl ue gases leaving the appliance.

Forced Draft - Combustion air supplied under pressure to the fuel burning equipment.

Gas Connector Assembly - A semi-rigid or fl exible connection between the gas line and the burner control assem-

bly. This includes a shut-off valve with a 1/2” female pipe connection.

Halogenated Hydrocarbon Compounds - Hydrocarbon, compounds which contain halogen elements such as hydro-

gen, chlorine, fl uorine, bromine, and iodine. These are generally non-corrosive until after being heated at several

hundred degrees (as during a combustion process). At this point a decomposition takes place, freeing halogen com-

pounds. When these compounds are combined with moisture for combustion products, extremely corrosive acids

are formed.

Heat - A form of energy that is exchanged between a system and its environment or between parts of the system

induced by temperature difference existing between them.

Heat Gain - The quantity of heat absorbed by an enclosed space or system.

Heat, Latent - Change of enthalpy during a change of state.

Heat Reservoir - An ideal system that can absorb or reject an indefi nitely large amount of heat.

Heat, Sensible - Heat that causes a change in temperature.

43


Heat, Specifi c - The ratio of the quantity of heat required to raise the temperature of a given mass of any sub-

stances one degree to the quantity required to raise the temperature of an equal mass of a standard substance

(usually water at 59O F (15O C)) one degree.

Heating Value, Higher (HHV) - The heat produced per unit of fuel when complete combustion takes place at con-

stant pressure and the products of combustion are cooled to the initial temperature of the fuel and air when the

vapor formed during combustion is condensed.

Heating Value, Lower (LHV) - The gross heating value minus the latent heat of vaporization of the water vapor

formed by the combustion of the hydrogen in the fuel.

Induced Draft - Drawing air from the combustion chamber by mechanical means.

Inductive Load - An alternating current load in which current lacks voltage.

Infi ltration - The uncontrolled inward air leakage through cracks and interstices in any building element around

windows and doors of a building, caused by the pressure effects of wind or the effect of differences in the indoor

and outdoor air density.

Lanced Stop - A tab in the lined coupling used to prevent racking of the coupling when driving lock member. (Pro-

vided on all couplings produced after July 1979).

Liquefi ed Petroleum Gases - The terms “Liquefi ed Petroleum Gases”, “LPG” and “LP-Gas” include any material

which is composed predominantly of any of the following hydrocarbons, or mixtures of them; propane, propylene,

butanes (normal butane or isobutane), and butylenes. This high heating value gas is stored under high pressure in

liquid form.

Make-up Air - Air brought into a building from the outside to replace that exhausted.

Mean Radiant Temperature (MRT) - The single temperature of all enclosing surfaces which would result in the

same heat emission as the same surface with various different temperatures.

Orifi ce - The opening in an orifi ce cap, orifi ce spud, or other device whereby the fl ow of gas is limited and through

which the gas is discharged.

Orsat Apparatus - A gas analyzer based on absorption of CO2, O2, etc. by separate chemicals that have a selective

affi nity for each of those gases.

Power Burner - A burner in which either gas or air, or both, are supplied at pressures exceeding, for gas, the line

pressure, and for air atmospheric pressure, this added pressure being applied at the burner.

Primary Air - The air introduced into a burner which mixes with gas before it reaches the port(s).

44


Pyranometer - An instrument that measures the combined direct and indirect radiation by means of a calibrated

sensing element.

Radiant Branch - A section of radiant pipe with one or more burners fi ring in series which is connected to the tail

pipe.

Radiation - The transfer of energy in wave form for a hot substance to another independent substance cooler in

temperature with no material means of heat transfer.

Radiant Tube - That section of tubing run between burners and up to 50 feet (depending upon burner size) down-

stream from the last burner in a series. This tubing is of hot rolled steel.

Refl ector - A device conFigured to direct radiant energy to the point of use in the space while absorbing little en-

ergy.

Refl ector Support - A device that orients and maintains refl ector position.

Residential Application - Providing comfort heating for single family living quarters.

Resistive Load - (1) An electric load without capacitance or induction, or one in which inductive portions cancel

capacitive portions at the operating frequency. (2) An electric load with all energy input converted to heat.

Single Fuel Burner - This is the standard burner in which the pilot and main orifi ces can be changed to fi re with

either natural gas or propane. No change is required in the regulator settings.

Stack - (1) A structure that contains a fl ue, or fl ues, for the discharge of gases. (2) The vertical train of a system of

soil, waste, or vent piping extending through one or more stories.

Stack Effect - The impulse of a heated gas to rise in a vertical passage such as in a chimney, small enclosure or

building due to density differences.

Stack Gases - The mixture of fl ue gases and air that enters the draft diverter, draft hood, integral draft diverter or

stack.

Stainless Steel - Any of several steels containing 12 to 30 % chromium as a principle alloying element; they usually

exhibit passivity in aqueous environments; providing corrosion resistance. Typical emissivity (e) = 0.45.

Stoichiometric Combustion (Perfect Combustion) - Fuel burning completely; all combustibles are consumed with

no excess air. Only the theoretical amount of oxygen is used (chemically correct ratio of furl to air).

Stratifi cation - Division into a series of graded layers, as with thermal gradients across a stream.

Tail Pipe - That section of tubing connecting the last section of radiant tubing in a series of burners to the vacuum

45


pump. This tubing is porcelain lined.

Shared - A section carrying the fl ow of combustion gases of more than one radiant branch.

Unshared - A section carrying the fl ow of combustion gases on only one radiant branch.

Therm - A quantity of heat equal to 100,000 BTU.

Thermal Expansion - Increase in or more of the dimensions of a body, caused by a temperature rise.

Thermostat - (1) Automatic control device, responsive to temperature, used to maintain a constant (static) tem-

perature. (2) A temperature-activated switch. (3) An instrument that responds to changes in temperature, and

directly or indirectly controls temperature. (4) A temperature sensitive device that automatically opens and closes

an electric circuit to regulate the temperature of the space with which it is associated.

Tube and Refl ector Hanger - A device for supporting heat exchanger and refl ector.

U - Factor - The time rate of heat fl ow per unit area under steady conditions from the fl uid on the warm side of a

barrier to the fl uid on the cold side, per unit temperature difference between the two fl uids. It is evaluated by fi rst

evaluating the R - value and then computing its reciprocal.

U Factor - Fuel use factor per 1000 BTU/hr calculated heat loss.

Vacuum Pump System - A complete combustion system consisting of a vacuum pump, burners, 1 control panel,

thermostats and 4 inch O.D. steel tubing for heat exchanger surface in the form of radiant and tail pipe plus as-

sorted refl ectors and other hardware. The number of such systems required is based primarily on the heat loss of

the building.

Vacuum, End Vent - Vacuum measurement taken at the beginning of a radiant branch (the end vent) on a CORAY-

VAC® System.

Vacuum, Orifi ce - Vacuum measurement taken at the orifi ce access plug on a CO-RAY-VAC burner.

Vent / Air Intake Terminal - A device which is located on the outside of a building and is connected to a furnace,

boiler or heater by a system of conduits. It is composed of an air intake terminal through which the air for combus-

tion is taken from the outside atmosphere, and an exhaust terminal from which fl ue gases are discharged.

Vent Pipe - Passages and conduits in a direct vent system through which gases pass from the combustion chamber

to the outdoor air.

Zone (Control Zone) - A space or group of spaces within a building with heating or cooling requirements suffi ciently

similar that comfort conditions can be maintained by a single controlling device.

46


Glossary ReferencesAmerican National Standard for Gas Fired Infrared Heaters, ANSI Z83.6-1982

American Gas Association, Cleveland, Ohio, 1982.

North American Combustion Handbook, 2nd Edition

North American Manufacturing Company, Cleveland, Ohio 1978.

Terminology of Heating, Ventilation, Air Conditioning and Refrigeration.

American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc., Atlanta,

Georgia, 1986.

4.0 Radiant Heating Design Issues

In order to insure successful application of radiant heating appliances, a number of design issues must be consid-

ered. Proper utilization of the inherent performance advantages of radiant heating depends heavily on a thorough

analysis and understanding of the application space, its utilization, and the expected benefi ts from the radiant

heating system. In essence, what is to be accomplished? What are the requirements of the application? How will

the radiant heating system interface with the occupants, scheduling parameters and activity level? These questions

and others must be answered to properly execute the design thought process. Additional issues, among them

• Utilization factors,

• Radiant adjustment to heat loss, and

• Height adjustment for radiant energy can effect the design approach. These issues are discussed

briefl y below.

4.1 Utilization Factors

Consideration must be given to the utilization parameters for a particular application. Of major importance in such

a consideration is the determination of an accurate heating load (heat loss) calculation. The American Society of

Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) has well documented methods for determining

the heating load (See ASHRAE Handbook of Fundamentals - 1985, ch. 25). The importance of an accurate heat loss

cannot be over emphasized, as the best equipment designs can be rendered ineffective if poorly applied. Areas of

special concern in determining heat loss relate to:

• Accurate constructional descriptions

• Air change estimation to determine infi ltration loss

• External factors (such as proper design temperature, wind velocity and direction)

• Internal heat gains

• Additional heating load to compensate for cold masses (for example, machinery or trucks)

In addition to an accurate heating load, special consideration must be given to allow for radiant effects (as com-

pared to conventional air heating). The realization that maximum comfort is only achieved by providing warm

surfaces which exchange gentle, well distributed radiant energy with the occupants, will insure a successful radiant

heating application. Additionally, possible radiant shadows cast by beams or pillars can effect proper placement of

the radiant appliance.

Heaters should be located suffi ciently inboard of exterior walls to prevent direct radiation from the heater from

contacting the wall and being lost to the outside. Page 54, Figure 21 represents graphically the relationship of radi-

ant output intensity to horizontal distance D from center line of burner emitter for a burner mounted at height H.

Distance D from center line is given in multiples of mounting height H. As shown, for distance D greater than 1.5H

the intensity drops below 50 % of the intensity at center line (D=O). As a practical limit, radiant appliances with

48

Radiant Heating Design Issues

high fi xture effi ciency should be located no closer to exterior walls than 1.5 times the mounting height.

, Figure 21 can also be used to estimate the coverage capability of a radiant heating appliance. (See Section

4.1.1 below for more information on coverage). The specifi c application will determine the degree of coverage is a

major issue when applying radiant heating appliances to station heating (spot heating).

Note, relationships illustrated on Page 33, Figure 15 relates to a deep dish, high fi xture effi ciency radiant system.

4.1.1 Coverage

Page 55, Figure 22 demonstrates the physical coverage differences between a well distributed,

multiple burner system and a single large burner. Because fl oor temperature rise is a major

contributor to comfort, a well distributed pattern (high pattern effi ciency) is desired to expose as

high as a percentage of fl oor area as possible to direct radiant energy. (See Page 90, Figure 38, Page

81, Section 7.1 for additional information).

It is evident from Page 55, Figure 22 that a well distributed energy pattern can satisfy the

requirement for maximum comfort more effectively than a large output (from a single burner)

energy pattern.

49


Inte

nsit

y Va

riat

ion

wit

h W

idth

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50


Coverage Comparison(Equal BTU Input and Constant Mounting Height)

Single Burner, Concentrated Pattern, Low Pattern Effi ciency

Multiple Burner, Even Pattern, High Pattern Effi ciency

Figure 22

51


4.2 Radiant Adjustment to Heat Loss

The practice of applying an adjustment factor to heat loss calculations for radiant heating systems is well known

within the radiant heating industry, having been used by manufacturers for over 25 years. Recently, a number of

studies have been conducted to identify the values of the adjustment factor in the range of 0.8 to 0.85 (ASHRAE

Transactions Volume 93, part 1). This adjustment can be more thoroughly understood when considering the follow-

ing radiant effect issues.

• Infrared energy heats objects, not the air;

• Lower ambient air temperatures reduce the amount of air infi ltration;

• Less air stratifi cation with radiant heat;

• Lower ambient air temperatures reduce the transmission heat loss across walls and roof;

• Elevated fl oor temperatures provide a thermal reserve capacity;

• Increased mean radiant temperature allows the occupants to perceive thermal comfort at

the reduced air temperature.

Each of these issues impact favorably on the utilization of the installed capacity of the radiant heating system. This

fact, together with realization that the ASHRAE heat loss calculation methods (particularly the transmission heat

loss coeffi cients) have been developed specifi cally for conventional hot air systems, demonstrates the need for the

heat loss adjustment factor.

4.3 Radiant Height Adjustment Factor

As discussed above in Section 4.2, the installed capacity of radiant heating systems is typically reduced compared

to the calculated heat loss due to the radiant effects associated with a properly designed radiant heating system.

The ability of a radiant system to provide the advantages of these radiant effects rests largely with the ability of

this system to establish a reserve heat capacity in the fl oor. Without this reserve capacity, radiant comfort cannot

be achieved. (The exception is in station heating / spot heating applications where suffi ciently high levels of direct

radiation are received from the heater.) The height adjustment factor is a means to insure adequate fl oor level ra-

diant intensity to “charge” the fl oor heat reservoir. , 59, 58, and 60 illustrate the relationship of fl oor level

intensity to height for single and multiple (overlapping) burner runs incorporating a high fi xture effi ciency system.

52


Calculated Intensity Chart(Single Burner Runs, High Fixture Effi ciency Equipment)

Table 1

53


Burner Location for Intensity Charts(Single Burner Run)

Where H = Mounting Height

D = Horizontal distance from center line of burner emitter (at fl oor level)

��

;

A��:#��*�;

5�,��

Figure 23

54


Where I = - Intensity at the fl oor directly below center line of a burner mounted at 16 ft.

- This calculation assumes 100% of the output will be allocated to a fl oor area

as defi ned by a 120O pattern width.

- The values shown include the overlap and are minimum values with at least

two rows of burners on either side. The values of intensities are less between

all other rows.

- With spacing of 3.0 H between rows, the added intensity from adjacent rows

of burners is less than 5%.

Calculated Intensity Chart(Multiple Burner Runs, High Fixture Effi ciency Equipment)

Table 2

55


Where D = Horizontal distance between burner runs.

Burner Layout for Intensity Chart(Multiple Burner Runs)

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5AA7+7!85/)!-�

Figure 24

56


Additionally, higher mounting heights for radiant heating appliances increase the probability for direct radiant en-

ergy loss due to exposure of longer wall surfaces. Proportionately larger wall surfaces also remove energy from the

fl oor to a larger degree, decreasing fl oor heat reservoir.

The increased input capacity recommended by a height adjustment factor is not extraneous as compared to the

heat loss calculation. Rather, it is a realization that in order to maintain radiant comfort conditions (and the eco-

nomic benefi ts) a minimum radiant level must be maintained at the fl oor.

It is recommended that an adjustment to the heat loss of 1% per foot for mounting heights above 20 feet be added

up to 50-60 feet. Above this height, additional correction overstates the BTU requirement as determined by the

heat loss.

Below are two examples of how to implement the height adjustment factor.

Example 1

• Mounting Height 30 feet

• Thermal effi ciency 80%, therefore 0.85 radiant heat loss adjustment used.

• Calculated heat loss 350,000 BTU/HR.

Heat Loss = 350,000 BTU/HR

Radiant Adjustment x .85 BTU/HR

297,500 BTU/HR

1%/FT Height Adjustment

(30ft - 20ft = 10%) x 1.1

327,250 BTU/HR Installed Capacity Required

57


Example 2

• Mounting Height 60 feet

• Thermal effi ciency 90%, therefore 0.80 radiant heat loss adjustment used.

• Calculated heat loss 500,000 BTU/HR.

Heat Loss = 500,000 BTU/HR

Radiant Adjustment x .8 BTU/HR

400,00 BTU/HR

1%/FT Height Adjustment

(60ft - 20ft = 40%) x 1.4

560,000 BTU/HR Installed Capacity Required

(Note in example 2, if equipment had been conventionally sized based on thermal output only, a nearly identical

input requirement would result.) For mounting heights above 50-60 feet, no further correction is generally neces-

sary provided:

• The fl oor level radiant intensity is suffi cient to establish a reserve heating

capacity (hence radiant comfort);

• The heat loss requirement is satisfi ed based on thermal output.

For additional information on specifi c application, the manufacturer should be consulted.

5.0 Radiant Heating Application Issues

Previously, on Page 52, Section 4 a number of areas relating to successful radiant heating design issues were dis-

cussed. Equally infl uential to the success of a radiant heating system are a number of application issues that relate

the function of the radiant heating system to the application. Following are areas that must be considered when

determining how effective a radiant system will be, once installed:

• Parameters for comfort.

• Design input levels, and how they relate to comfort.

• Control philosophy with radiant heating.

• Installation considerations.

• Occupancy

Each of these issues is described below in more detail.

5.1 Parameters for Comfort

Comfort is an environmental quality easily recognized when it is experienced. However, it is more diffi cult to defi ne

comfort in such a way that it can be used to control the thermal environment in an industry or commercial appli-

cation. Comfort is associated with a neutral thermal sensation during which the human body regulates its internal

temperature with a minimum of physiological effort. Relative to the radiant heating industry, perceived comfort,

temperature and thermal acceptability are relative to an individual’s metabolic heat production, its transfer to the

environment and resulting physiological adjustments. The heat transfer is infl uenced by the environmental factors

of:

• Air Temperature

• Thermal Radiation

• Air Movement (velocity)

• Humidity

and by the personal factors of:

• Activity

• Clothing

ASHRAE Standard ANSI / ASHRAE 55-1981 provides a comprehensive technical explanation of the

interaction of these factors relative to comfort.

59

Radiant Heating Application Issues

A less technical description is provided herein. When designing radiant heating appliance systems for comfort, con-

sideration must be given to the following.

• Energy received by the occupant as radiation from the heating appliance.

• Energy received by the occupant from the fl oor (and other surfaces, if applicable due to re-radiation.

• Ambient air temperature.

Note that surfaces within a room (walls and roof) can substantially reduce comfort by “removing” radiant energy

from occupants.

Mean radiant temperatures (MRT) is a concept used to describe the net amount of radiant energy available to pro-

vide comfort. MRT is defi ned as the uniform surface temperature of a black body enclosure in which an occupant

would exchange the same amount of radiant heat as in the actual nonuniform space. Very roughly, MRT can be indi-

cated by an average of the fl oor, walls and ceiling temperatures. It is for this reason that suffi ciently warmed fl oors

with reserve heating capacity are required if a comfort condition is to be realized in application of radiant heating.

The ANSI/ASHRAE Standard 55-1981 defi nes another quantity, operative temperature, to defi ne comfort. For low air

velocities (below 80 FPM), operative temperature is described as the average of air temperature (+a) and MRT as

follows:

ta + MRT

2

Where to = Operative temperature

ta = Air Temperature

MRT = Mean Radiant Temperature

The comfort chart (Ref. ANSI Standard 55-1981, Figure 2) indicates comfort ranges for operative temperatures:

• In Summer from 73O F to 81O F

• In Winter from 68O F to 71O F

Note these ranges are for varying conditions of humidity.

Generally speaking, an operative temperature of approximately 70O F is considered comfortable during heating

season. Variation to this can occur depending on clothing and activity level.

With radiant heating properly applied, fl oor temperatures can be elevated as much as 10O F to 15O F as compared to

fl oor temperatures with conventional air heating. By re-radiation of energy from the fl oor, the corresponding walls

and inside roof surface temperatures are also increased.

to =

60


From this consideration of higher temperatures of inside building surfaces as obtained with radiant heating it is ap-

parent why the comfort level can be maintained with a lower air temperature with radiant heating.

Table 3, below, has been prepared to show the Air Temperature (+a) required under various conditions to achieve

comfort at (+o) of 70O F.

TABLE 3

Heating Method Temp. MRT Temp. +a Temp +o

Convective Air Heating 65O F 75O F 70O F

Radiant Heating 75O F 65O F 70O F

Section 5.2, below, discusses typical installed capacities to produce comfort in various applications.

5.2 Design Input Levels

Typical design input levels vary according to the type of heating that is required. Basic types of utilization are:

a) General space heat, including perimeter heating;

b) Area heating;

c) Spot or station heating;

d) Process heating.

As the installed capacity increases to match the desired utilization level (“a” through “d” above) comfort becomes

increasingly dependent on direct radiant output from the heating appliance.

, Figure 25 lists typical installed capacities for various utilization categories. These are tabulated for typical

values in varying climatic zones. For example, in an area with 6000 degree-days and typical design temperature rise

(80O F for this), an installed capacity from 25 to 50 BTU per Ft2 per Hr would provide adequate comfort for general

space heating.

For spot (station) or area heating, Page 67, Figure 26 indicates BTU output levels required for a given coverage as a

function or required comfort temperature rise. The required input level may be calculated as follows:

Output Level

Radiant Effi ciency

Page 68, Table 4 lists input levels for spot or area heating as a function of air temperature, air velocity and activity

level.

Note that for heating areas or spot stations, it is essential that the radiant heating appliances provide energy from

at least two (preferably three) directions, none of which are directly overhead.

Inside Surface Air Operative

= Input Level

61


5.3 Control Philosophy

Night setback is a well known, accepted method of conserving fuel in the heating industry. Because radiant heating

does not utilize the same mechanisms as convective air heat to provide comfort in a space, the concept of night

setback must be treated differently.

Because of the importance in maintaining a fl oor heat reservoir to provide comfort with radiant heating, night set-

back must be accomplished is such a manner so as not to deplete the fl oor heat “charge.”

When determining the setback parameters, consideration must be given as to the degree direct radiant output from

a radiant heating appliance provides space comfort. As a space increases its dependence on direct radiant output

for comfort (as in spot heating), setback can be increased. In buildings that do not have large levels of fl oor inten-

sity (as in high bay buildings), setback should be minimized.

Below is a summary guide for setback parameters for various applications.

Application Recommended Setback OF

• High Bay Areas Very little to none

• Average Construction Commercial Buildings Up to 5O -7O F

• New Construction Commercial Building Up to 8O - 10O F

Assumes - Typical Design Temperatures rise for each Degree Day Level.

- Radiant Effi ciency range 35 - 60%

Typical Range of Installed Capacity Requirements(BTU/Ft2 - Hr) for Various Application Types*

Figure 25

62


Figure 26

Output Levels for Comfort in Spot or Area Heating

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63


Table 4

64


5.4 Installation Considerations

Prior to the design, the thought process should focus on extraordinary factors possibly existing in the building’s us-

age. Is there potential hazardous or corrosive vapors present? Is there combustible merchandise being stored up or

near the roof line? Is it feasible to recess the radiant heating system in a drop ceiling for more suitable aesthetics?

Is it practical to install radiant heating in a public forum where codes require high levels of ventilation?

Hazardous Environment:

Referencing national and local fi re codes can quickly determine the suitability of individual radiant heating sys-

tems. In buildings where occasional vapors may be present, it is prudent to consider application of fresh air sup-

ply to create an independently enclosed system, which does not ingest building air. Use of cooler outside air can

decrease thermal effi ciency slightly and should be considered only when necessary.

Corrosive Environment:

Occasionally such products as cleaners, preservatives, refrigerators, etc. can contain corrosive contaminants

which are harmful to any heating system. Just traces of fl uore/chloro hydrocarbons in the building atmosphere can

greatly accelerate the rate of corrosion on heat exchanger surfaces. To protect against such deterioration, a fresh

air supply is recommended.

Safety:

With any heating source, consideration must be given to performance related items, such as the clearances to

combustible materials defi ned by all laboratories during the appliance’s certifi cation process. Attention should be

focused on such situations as stacking of combustible products, penetration of combustible walls, and proximity

of materials to the radiant fi xture. In most cases, a solution is available by application of uniquely designed side

refl ector, universal shield, triple wall thimble or other specialty items. The thought process should include sensitive

consideration of confi guration and location of the radiant tube heaters during the design phase.

Aesthetics:

Often radiant heating is preferred in large expanses of low ceiling areas in decorative form such as showrooms,

stores, theatres, bowling alleys and classrooms. With the advent of low rated output radiant burners, 2’ x 4’ metal

ceiling mesh, and side refl ector, these applications have received wide acclaim as safe, effi cient, and cost effec-

tive.

Ventilation:

Such public facilities as civic centers, shopping mall commons, theatres and gymnasiums are fundamentally sound

applications for radiant heating systems because of the high effi ciency yield and even distribution of comfort. Even

as codes require a high volume of air change, the application of radiant heating with roof-top makeup air units is

65


considered more functional when comparing cost of operation. Often public occupancy time represents less than

20% of the day, leaving 80% duty to the more cost effi ciency radiant system. Further, radiant systems can typi-

cally be sized to handle up to three air change volumes each hour, requiring less heat makeup with the coded air

volume.

5.5 Occupancy

Of major importance during the design stages of a radiant heating system is a consideration for the occupancy of

the building in question. As discussed, personal factors such as activity and clothing level can greatly infl uence

the perception of comfort for the occupants. Occasionally, a particular sensitivity to comfort can be identifi ed for

intended occupants of a structure, and these specialized needs must be addressed to insure a satisfactory applica-

tion. Examples of these types of sensitive installations are:

• Zoos

• Kennels

• Residences for the elderly

Fitting the design concept to the requirement of the building and its components can insure a successful applica-

tion.

6.0 Fuel UtilizationRadiant heating has long been recognized as a cost effective method of providing heat. Determining fuel utiliza-

tion characteristics for radiant heating is possible utilizing accepted ASHRAE methods. Because of this, fuel usage

comparisons to conventional heating equipment can also be made.

Section 6.1 derives the necessary equations to calculate fuel usage. Because this calculation is applied to a design

(maximum) heating load, and is subject to errors from a number of other sources, namely:

1. Difference between historical and actual degree day numbers,

2. No consideration for the effects of internal heat gains (from lights, etc.),

3. Differences between estimated and actual air change or ventilation heat loss,

The estimated annual fuel usage calculated is usually conservative. ASHRAE has recently implemented a correction

coeffi cient CD, based on degree-days, to provide for more realistic fuel use estimates.

It is necessary to recognize the range of values that can exist for the fuel utilization factors, depending on appli-

cation circumstances. As an application increases it’s dependency on radiant energy to provide comfort, a corre-

spondingly larger fuel savings can be expected over conventional heating equipment.

Page 77, Section 6.2 gives a comparative analysis for various types of heating equipment and includes consideration

for operating costs as well as fuel costs.

67

Fuel Utilization Analysis

U1 = (EQ 2A)

6.1 Formula Derivation

1. Formula Defi nition Roberts-Gordon (RG) vs. ASHRAE

(Reference ASHRAE 1985 Fundamentals pp. 28.2 - 28.3)

A) (RG) Formula

U1 x Nb X D 70O

1000 x DTR

Where F = Estimated Annual Fuel Consumption (units same as U1)

U1 = Factor for Fuel unit usage per Unit Heat Loss Nu

Nb = Calculated Heat Loss at design temperatures

D = Number of Degree Days Annual

DTR = Design Temperature Rise

CD = Empirical corrections factor for heating effect vs 65O F degree days, usually less than 1.0

and based on actual degree day (from Page 75, Figure 27)

U1 Factor Defi nition Formula:

Nu x C 24

E x 70O x V

Where Nu = Unit heat loss of 1000 BTU/HR with temperature rise of 70O

C = Experienced base correction factor based on reduction of ASHRAE calculated heat loss due to radiant

effects.

E = Thermal Effi ciency

V = Heating value of fuel used to defi ne F in terms of fuel units rather than BTU

Substituting Nu into EQ 2

1000 BTU/HR x C x 24

E x 70O x V

When EQ 1 and EQ 2A are combined:

1000 x C x 24

E x 70O x V

1000 x DTR

F = (CD) (EQ 1)

U1 = (EQ 2)

F = (CD)

x Nb x D 70O

68


F = (CD) (EQ 3)

Simplifying:

C x 24 x Nb x D

E x DTR x V

B) Compare to ASHRAE Formula (pp, 28.2 - 28.3 Fundamental Handbook 1985):

HL x D x 24

t x K x V

Where E = Fuel or energy consumption ( = F in RG terminology)

HL = Calculated Heat Loss ( = Nb in RG terminology)

D = Degree Days ( = D in RG terminology)

t = Design temperature rise ( = DTR in RG terminology)

K = A correction factor that includes effect of effi ciency and other load performance factors ( = E/C in

R-G terminology)

CD = Empirical correction factor for heating effect vs 65O F degree days usually less than 1.0 and based on

actual degree day

V = Heating value of fuel used to defi ne E in terms of fuel units rather than BTU

Substituting RG terminology into EQ 4:

Nb x D x 24

DTR x E/C x V

Rearranging EQ 5:

C x 24 x Nb x D

E x DTR x V

Note that EQ 3 and EQ 6 are identical. Values of (CD) can be read from Page 75, Figure 27 at the appropriate degree

day value.

2. U1 Factors Calculation (Using EQ 2)

A) CRV - B Series

Where C = 0.7, E = 0.90, V = 1000 for Natural Gas.

1000 x .7 x 24 CF

0.90 x 70 1000 1000 BTU/HR Heat Loss

F = (CD) (EQ 4)

F = (CD) (EQ 5)

F = (CD) (EQ 6)

U1 = = 0.267

69


U1 = = 0.293

U1 = = 0.457

U1 = = 0.307

U1 = = 0.386

U1 = = 0.395

U1 = = 0.317

B) CRV - E Series


1000 x .7 x 24 CF

0.82 x 70 1000 1000 BTU/HR Heat Loss

C) VANTAGE


1000 x .7 x 24 CF

0.78 x 70 1000 1000 BTU/HR Heat Loss

D) UNIT HEATERS


1000 x 1.0 x 24 CF

0.75 x 70 1000 1000 BTU/HR Heat Loss

E) DIRECT FIRED MAKE-UP AIR


1000 x 1.06 x 24 CF

0.92 x 70 1000 1000 BTU/HR Heat Loss

(NOTE: C & E Factor for direct fi red make-up air are defi ned for average winter temperature of 55O F and 8% nonre-

coverable latent heat due to inability to condense all combustion fl ue products. This is for purposes of the example

to follow).

F) AIR ROTATION


1000 x .9 x 24 CF

0.80 x 70 1000 1000 BTU/HR Heat Loss

G) HIGH INTENSITY


1000 x .85 x 24 CF

0.92 x 70 1000 1000 BTU/HR Heat Loss

NOTE: Additional U1 factors for other equipment and fuel are tabulated on Page 76, Figure 28.

70


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71


Figure 28

Fuel Utilization (U1) FactorsEquipment Fuel/Units Factor 1/K ( = C/E) Per Degree Day

CORAYVAC® B/A Natural Gas/CF .778 .267 CF

CORAYVAC® E Natural Gas/CF .854 .293 CF

Vantage Natural Gas/CF .897 .307 CF

Gordon-Ray Natural Gas/CF .897 .307 CF

High Intensity Natural Gas/CF .924 .317 CF

Unit Heater Natural Gas/CF 1.334 .457 CF

Direct Fired Make-Up Air: (Note 1)

Outdoor Temp. 0O F Natural Gas/CF 1.609 .555 CF



Air Rotation Natural Gas/CF 1.125 .386 CF

Central Furnace Natural Gas/CF 1.429 .490 CF

Boiler Natural Gas/CF 1.538 .527 CF

CORAYVAC® B/A LP/Gallons .778 .00300 GAL.

CORAYVAC® E LP/Gallons .854 .00320 GAL.

Vantage LP/Gallons .897 .00336 GAL.

Gordon-Ray LP/Gallons .897 .00336 GAL.

High Intensity LP/Gallons .924 .00345 GAL.

Unit Heater LP/Gallons 1.334 .00499 GAL.

Air Rotation LP/Gallons 1.125 .00433 GAL.

Boiler LP/Gallons 1.538 .00575 GAL.

Unit Heater Oil/Gallons 1.429 .00350 GAL.

Central Furnace Oil/Gallons 1.538 .00376 GAL.

Boiler Oil/Gallons 1.667 .00407 GAL.

Assumptions: Natural Gas 1,000 BTU/CF

L.P. 91,500 BTU/GAL

#2 Oil 140,000 BTU/GAL

Electricity 3,413 BTU/KWH

NOTE 1: The U1 factor is based on useful heat available after heating the required ventilation rate of 4 CFM per 1000

BTU/HR of input. If this level of ventilation U1 Factor for Natural Gas .373 and the outside air temperature is not a

consideration.

Correction U1 Factor

72


6.2 Illustrative Example

1. Operating Expenses Include Both

a) Fuel Usage Costs

b) Electric Usage and Demand Costs

A) Fuel Usage Costs

Fuel usage can be determined via (EQ 1) by utilizing U1 factors as derived above.(Page 76, Figure 28), As

previously stated, (EQ 1) is interchangeable with accepted ASHRAE procedures.

Fuel usage costs are determined by the following:

CF = F x A (EQ 7)

Where CF is total annual fuel cost

F is estimated annual fuel consumption

A is cost per fuel unit (units consistent with F)

B) Electric Usage Costs (usage and demand)

To determine electric usage costs, an estimate of equipment running time must be made. This can be

accomplished as follows:

DD x 24

DHR

Where TR = Estimated annual equipment running time

DD = Degree Days

DHR = Estimated average degree rise hours per hour (determined by operating conduction)

Example:

For a typical warehouse:

8 hour (day shift)

1st hour: 10O rise (from night setback to day set point) = 10O - HRS.

2nd - 8th hours: 5O rise x 4 cycles per hour = 5 x 4 x 7 = 140O - HRS.

16 hour (night shift)

1st - 2nd hours: no equipment run time (building cools)

3rd - 16th hours: 5O rise x 4 cycles per hour = 5 x 4 x 14 = 280O - HRS.

TR = (EQ 8)

73


10 + 140 + 280

24

= 18 degree - hours/hour

Using (EQ 8), determine TR for Dallas, TX: (to conform to example below)

TR = = 3209 HRS. Estimated annual equipment running time.

Electric usage and demand costs are determined by:

CE = (L x TR x KWC) + KWD (EQ 9)

Where CE = Total annual electric cost

L = Equipment connected electric load

TR = Estimated annual equipment running time

KWC = Cost per electric unit (units consistent with L)

KWD = Demand charge per electric unit (units consistent with L)

2. Comparative Analysis for Illustrative Purposes

Assumption for analysis:

Location: Dallas, Texas

Degree Days: 2407

Design Temperature Rise: 48O F (68O F inside, 20O F outside)

Transmission Loss Factors:

Walls U = .65

Roof U = .35

Doors U = .65

Room Size: 400ft x 250ft x 22ft ceiling

Infi ltration Rate: 1/3 ACPH (or approximately 12,100 CFM)

CD = 0.76 (For 2407 Degree Days - From ASHRAE Chart, Page 75, Figure 27

HEAT LOSS CALCULATED PER ASHRAE PROCEDURE (See , Figure 29)

Cost of Natural Gas = $0.40 per therm

Cost of Electric Usage = $0.05 per KWH

Using equations and factors previously derived as noted, comparative analysis is tabulated on Page 80, Figure 30.

Average degree hours =

2407 x 24

18

74


Job: “Sample Warehouse Cost Study”Figure 29

LENGTH 400 WIDTH 250 HEIGHT 22 TEMP 68 TEMP 20 TEMPRISE 48

Btu/HR

INFILTRATION: NUMBER OF AIR CHANGES .33 * VOLUME * DTR = 627,264

MECH. EXHAUST: CFM * 1.08 = 0 * DTR = 0

FLOOR LOSS: PERIMETER * FACTOR (INSULATED = 0.55, = 50,544

UNINSULATED = 0.81) * DTR

INFILTRATION PLUS FLOOR LOSS = 677,808

SURFACE QUANTITY * WIDTH * LENGTH = AREA * “U” = * DTR =

INSIDE OUTSIDE DESIGN

Transmission Heat Loss 2,572,320 Btu/Hr

Total Calculated Heat Loss 3,250,128 Btu/Hr

75


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0

7.0 Appliance Approach to Market Place

7.1 Characteristics for Performance

Ever since the late 1950’s, radiant heating has been synonymous with fuel effi ciency and uniform comfort in com-

mercial, industrial, and agricultural applications.

The radiant heater which pioneered the transition from warm air heat to “heat on the feet” comfort, provided

uniform distribution of radiant energy onto the total fl oor area by means of multiple burners in series. Its high ef-

fi ciency was the result of its better emitter surface averaging 1.0 square feet per thousand BTU input, operated

under vacuum in a condensing mode. CORAYVAC® by Roberts Gordon, LLC

remains the most recognized radiant heater in the ever expanding market place, and has set the standards for uni-

form comfort, operational effi ciency, longevity, and safety.

Through the years, and mainly for budgetary considerations, many different types of radiant tube heaters have

emerged to provide broad choices in cost, effi ciency and radiant distribution, See Page 83, Figure 31.

In tier one, there remains only one high effi ciency radiant heater with multiple burners in series that operates in

the condensing mode, and is rated at over 90% effi ciency (Type 1(b)), See Page 84, Figure 32.

In the second tier, several radiant heaters are available in the 80% effi ciency range. Operated in the dry, non-con-

densing mode, they usually are conFigured with multiple end burners connected to a power exhauster, and provide

an emitter surface from .42 to .61 square feet per thousand BTU input. (Quasi 1(b)/1(c) type).

A third tier of radiant tube heater falls within the 75% effi ciency range. They are conFigured as single burners under

power of draft venting, and provide emitter surface from .28 to .50 square feet per thousand BTU input. They are

either factory or fi eld assembled. (Quasi type 1(b)/1(c) or type 1(c)).

Differentiating the various types of radiant tube heaters requires understanding of products and knowledge of

materials used to best accomplish its design performance, See Page 84, Figure 32. Stainless steel is an impressive

material, but what is it emissive and refl ective value? Understanding the grade and character of aluminized tube,

has it been heat treated to effectively nearly double its emissive power? Is black paint applied to emitter tube

functional if its longevity is only 12 to 18 months. Since convective heat is substantially undesirable, is the refl ector

contour deep and broad enough to prevent its escape to the ceiling (stratifi cation)?

Is there suffi cient angularity to the refl ector top to prevent radiant energy from reradiating back onto the emitter?

All these differences, and more, eventually determine whether a good or defi cient fi xture is present to produce and

control the required radiant effect over the long haul.

Since the inception of radiant tube heat, design for most applications has concentrated radiant distribution on total

fl oor areas without signifi cant heat stratifi cation between fl oor and ceiling, See Page 90, Figure 38. With radiant

77

Appliance Approach to the Market Place

heat covering becomes a secondary source of heat by absorption at no extra cost and quickly some energy into

convective heat. Additionally energy is reradiated to the objects in the space, contributing to comfort. Hence, air

temperature is substantially lower for comfort that is normally associated with warm air-convection heating. This is

the proven standard established by CORAYVAC®.

With the advent of other types of radiant tube heaters with much larger burner output and shorter emitter lengths,

the comfort principle requiring total span distribution of radiant energy cannot be satisfi ed. Consequently, perim-

eter and area distribution designs requires attention.

With suffi cient emitter length to cover only a perimeter distribution (outside walls), center areas of the building

remain that must await convectional heat coverage could be achieved by the costlier means of adding more output

(heaters) than the heat loss requires. Some radiant heater manufacturers provide side refl ector to direct some of

the perimeter radiant energy toward the center. Others suggest tilting the refl ector up to 45O to reach the center

area without considering the signifi cant loss of convection heat to the ceiling. The resulting substantial stratifi ca-

tion works counter to the radiant heat loss adjustment principle through increased transmission loss.

With even larger burner outputs and shorter emitter lengths, a third level of radiant distribution results in area

distribution design, See Page 90, Figure 38. This distribution pattern is the least effective for people comfort since

spotted areas of radiant and convective heat are intermixed creating identifi able discomfort zones, at least until

convective heat transcends the entire span of the building. Greater stratifi cation and fuel use occur in this design

than any other. Larger output burners also require greater attention in design to clearance to combustibles.

In evaluating the good-better-best approach to radiant product and its resulting comfort distribution patters, cer-

tain cost factors are of vital consideration. Judgements such as longevity (life of fi xture) and its resulting energy

savings pay back, value of employee comfort and its measure to productivity, value engineering and its cost / ben-

efi t ratio to type and performance of equipment selected are all signifi cant and justifi able considerations.

78


APPLIANCE SUMMARY TABLE

Figure 30

RATE HTG SURFACEMFG BTU/HR FT2/MTBU/HR

A 120 vb 105’ x 4” OD 20’ vp .92/OPT 1.09 OPT

A 120 vb 60’ x 4” OD vp .52

A 125 pb 40’ x 4” OD 10’ vt .34 OPT

A 75 pb 20’ x 4” OD .28 vt

B 130 vb 60’ x 3½” OD 30’ vp .42/OPT .63 OPT

C 75 vb 58’ x (3” + 6” OD) vp .61

C 100 vb 35’ x 3” OD vp .27

D 120 vb 80’ x 3½” OD vp .61

D 125 vb 45’ x 3½” OD 20’ vp .33/OPT .48 OPT

E 125 pb 50’ x 4” OD vt .42

F 125 pb 40’ x 4” OD 20’ vt .34/OPT .50 OPT

G 125 vb 50’ x 4” OD vt .42

H 75 pb 32’ x 3” OD vt .34

H 100 pb 12’ x 3” OD 13’ vp .09/OPT .20 OPT

I 125 pb 140’ x 4” OD vt .34

J 125 pb 40’ x 4” OD 10’ vt .34/OPT .42 OPT

K 125 pb 40’ x 4” OD 20’ vt .34/OPT .50 OPT

79


7.2 Appliance Comparison

APPLIANCE COMPARISON (A)

Figure 32

MANUFACTURER A A A

THERMAL EFFICIENCY 90% 80% 75%

EMITTER

(FIRST SECTION)

Size 20’ - 50’ x 4” OD 10’ x 4” OD 4’ x 4” OD

Material Hot Rolled Steel Heat Treated Aluminized Steel

Heat Treated Aluminized Steel

Gauge 16 16 16

Emissivity .8 .8 .8

(SECOND SECTION)

Size 65’ - 110’ x 4” OD 50’ - 70’ x 4” OD 16’ x 4” OD

Material Hot Rolled With Porcelain Hot Rolled Steel Hot Rolled Steel

Gauge 16 16 16

Emissivity .9 .8 .8

REFLECTOR

Size 5-27/32” x 14½” 5-27/32” x 14½” 5-27/32” x 14½”

Material Finished Aluminum Finished Aluminum Finished Aluminum

CONFIGURATION A A A

TYPE 1b Quasi 1b/1c 1c

80


APPLIANCE COMPARISON (B)

Figure 33

MANUFACTURER A B B


EMITTER

(FIRST SECTION)

Size 10’ x 4” OD 10’ x 3½” OD 10’ x 3½” OD

Material Aluminized Aluminized Spiral Steel

Painted Aluminized Spiral Steel

Gauge 16 22 22

Emissivity .8 .8 .8

(SECOND SECTION)

Size 10’ - 50’ x 4” OD 50’ - 80’ x 3½” OD 30’ x 3½” OD

Material Hot Rolled Steel Aluminized Spiral Steel

Painted Aluminized Spiral Steel

Gauge 16 22 16

Emissivity .8 .5 .5 - .8

REFLECTOR

Size 5-27/32” x 14½” 3¾” x 12¼” 3¾” x 12¼”

Material Finished Aluminum Finished Aluminum Finished Aluminum

CONFIGURATION A D D

TYPE 1c Quasi 1b/1c 1c

81


APPLIANCE COMPARISON (C)

Figure 34

MANUFACTURER C C D


EMITTER

(FIRST SECTION)

Size 7¾” x 3” OD 7¾” x 4” OD 10’ x 3½” OD

Material Painted Stainless Steel 304 Painted Stainless Steel 304 Aluminized Steel

Gauge 16 16 16

Emissivity .6 - .8 .5 - .8 .5

(SECOND SECTION)

Size 17¼” x 3” OD 23’ x 3½” OD 27¼ x 4” OD 70’ x 3½” OD

Material Mild Steel Aluminized Spiral Mild Steel Hot Rolled Steel

Gauge 14 22 16 16

Emissivity .8 .8 .8 .8

REFLECTOR

Size 5¼” x 11½” 5¼” x 11½” 4” x 14”

Material Stainless Steel 304 or Aluminum Stainless Steel 304 or Aluminum Polished Aluminum

CONFIGURATION C C D

TYPE Quasi 1b/1c Quasi 1b/1c Quasi 1b/1c

82


APPLIANCE COMPARISON (D)

Figure 35

MANUFACTURER D E F


EMITTER

(FIRST SECTION)

Size 10’ x 3½” OD 10’ x 4” OD 10’ x 4” OD

Material Aluminized Steel Aluminized Steel Painted Aluminized Steel

Gauge 16 12 16


(SECOND SECTION)

Size 35’ - 55’ x 3½” OD 20’ - 50’ x 4” OD 20’ - 50’ x 4” OD

Material Hot Rolled Steel Aluminized Steel Painted Aluminized Steel

Gauge 16 16 16


REFLECTOR

Size 4” x 14” 3½” x 19” 5½” x 11”

Material Polished Aluminum Polished Aluminum Polished Aluminum

CONFIGURATION D E F

TYPE Quasi 1b/1c 1c 1c

83


APPLIANCE COMPARISON (E)

Figure 36

MANUFACTURER G H H


EMITTER

(FIRST SECTION)

Size 10’ x 4” OD 10’ x 3” OD 10’ x 3” OD

Material Aluminized Steel Heat Treated Aluminized Steel


Gauge 16 16 16

Emissivity .5 .8 .8

(SECOND SECTION)

Size 20’ - 50’ x 4” OD 22’ x 3” OD 2’ - 15’ x 3” OD

Material Painted Steel Heat Treated Aluminized Steel


Gauge 16 16 16

Emissivity .8 .5 .8

REFLECTOR

Size 5” x 11” 5¼” x 18 1/8” 5¼” x 18½”


CONFIGURATION D E F

TYPE 1c 1c 1c

84


APPLIANCE COMPARISON (F)

Figure 37

MANUFACTURER I J K


EMITTER

(FIRST SECTION)

Size 10’ x 4” OD 10’ x 4” OD 10’ x 4” OD

Material Aluminized Steel PaintedAluminized Steel Aluminized Steel

Gauge 16 14 16

Emissivity .5 .5 - .8 .5 - .8

(SECOND SECTION)

Size 30’ - 50’ x 4” OD 10’ - 50’ x 4” OD 30’ - 50’ x 4” OD

Material Hot Rolled Steel Hot Rolled Steel Aluminized Steel

Gauge 16 12 16

Emissivity .8 .8 .5

REFLECTOR

Size 5” x 11” 6½” x 16” 6’ x 13½”


CONFIGURATION D B D

TYPE 1c 1c Quasi 1b/1c

85


Distribution LayoutsFigure 38

Total Span Distribution

- Provided by multiple burners

in series

Perimeter Distribution

- Provided by multiple end

burners

Area Distribution

- Provided by individual

burner

APPENDIX A:

ANNUAL DEGREE DAYS TOSELECTED BASES

This information is extracted from a publication entitled Degree Days to Selected Bases that is available

from the National Climatic Center, U.S. Department of Commerce, National Oceanic and Atmospheric

Administration.

87

Appendix A: Annual Degree Days to Selected Bases

88


89


90


91


92


93


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